Hot Seats is a series in which academics report from the UK’s most interesting marginal constituencies. Neil Matthews and John Garry report on Fermanagh & South Tyrone.

Very few voters will emerge from the polling booth on May 7 with the firm belief that they have personally swung the result in their chosen candidate’s favour. The overwhelming majority of seats contested in UK general elections have historically been safe.

But one constituency where there is nothing inevitable about the result is Fermanagh and South Tyrone (FST). In 2010, this rural seat in the south-western corner of Northern Ireland boasted the lowest majority in the entire UK, with Sinn Féin’s Michelle Gildernew the winner by a mere four votes.

At 0.01%, this is the fourth-lowest majority in all of post-war UK electoral history – and quite a change from the previous election in 2005 when this was the UK’s 158th most marginal seat.

Sinn Féin’s wafer-thin 2010 margin was the result of some curious competitive conditions. Westminster abstentionist Gildernew’s only credible rival for the seat, Rodney Connor, stood as a de facto “joint unionist” independent candidate – enjoying the endorsement of Northern Ireland’s two largest pro-union parties, the Democratic Unionist Party (DUP) and Ulster Unionist Party (UUP).

This unofficial pact between the DUP and UUP, with both parties withdrawing from the contest, was a clear attempt to avoid splitting the unionist vote. It also heralded a return to a policy of unionist unity in the constituency (first adopted in 1950 and infamously abandoned in 2001).

Meanwhile, appeals by Sinn Féin for the Social Democratic and Labour Party (SDLP) – the other main nationalist party in Northern Ireland – to stand aside were rejected on the grounds that a pan-nationalist pact would be “sectarian”.

The result was that even by the standards of Northern Ireland’s divided political scene, the 2010 contest in FST was pitched as a clear battle between “green and orange” or nationalists and unionists, with voters encouraged to ensure representation for “their” community regardless of existing party loyalties.

Slanging match

In many ways, the same ingredients and electoral logic exist to make 2015 as compelling a contest in FST as 2010 – and there is every chance that the constituency will top the UK league table of marginal seats once again.

In March 2015 the DUP and UUP announced, after six months of negotiations, that both parties had agreed the largest electoral pact in Northern Ireland politics since the 1980s. Part of this four-constituency accord sees the UUP provided a clear run in FST, with their candidate, Tom Elliott, the only unionist in the race.

Once again, this communal unity has not been matched on the nationalist side, with the SDLP steadfast in its opposition to “nakedly sectarian pacts” and refusing to withdraw its candidate, John Coyle. But even with Coyle in the running, this remains a fight between Sinn Féin and the combined UUP-DUP forces.

But there are some telling differences from 2010 too. The “unionist unity” candidate, Tom Elliott, is a former UUP leader whose reputation for belligerence could be the unionists’ undoing. Elliott is renowned for a tirade launched in the aftermath of the 2011 Northern Ireland Assembly election, in which he referred to Sinn Féin as “scum” and the Irish tricolour as “the flag of a foreign nation”.

He has been asked to clarify his position on the remarks on several occasions throughout the campaign, and Sinn Féin is likely to keep the spotlight on them from here to polling day. The party is worried there could be a lower nationalist turn-out than in 2010, and it clearly intends to use everything at its disposal to get apathetic nationalists to the polls.

Unlike the “independent” unionist candidate who ran in 2010, Elliott’s UUP affiliation also means there is no guarantee that DUP supporters will be willing to hold their noses and vote for a rival party. That reluctance is reflected in the low rate of vote transfers between the two parties in Assembly and Local Government elections, which are conducted using the single transferable vote system.

On the other hand, however, Elliott’s standing as a prominent Orange Order member – an institution held in especially high regard by DUP supporters – could help some of the warier DUP voters overlook his UUP credentials.

And since DUP supporters are more stridently unionist than their UUP counterparts, perhaps they will be more willing to put aside party political grievances and do what’s best for the unionist cause.

Whatever the outcome in FST in 2015, however, it is likely to be a very close run thing indeed. And with a margin of just four votes last time around, the Northern Irish parties’ mutual suspicion and disdain are in overdrive.